White light surface inspection systems have been developed for high throughput and highly automated manufacturing of products with decorative and technical surfaces. These systems facilitate a high degree of sensitivity to even the smallest changes in form and gloss level on a myriad of types of surfaces and finishes.
A conventional phase-shifted deflectometry setup 100 is shown in FIG. 1. The setup includes a surface 110 of an object under test, a pattern area 120 generated by an illumination unit (not shown), a camera 130, and an image evaluation unit 140 with a display. The camera 130 sequentially takes a plurality of images of the reflected pattern area, which are subsequently evaluated by the image evaluation unit 140.
The phase-shifted deflectometry setup shown in FIG. 1 requires the illumination unit, the camera, and the surface of the object under test to be in a fixed spatial location to each other while the plurality of images is taken by the camera.
A conventional device for optically inspecting a surface of a sample to determine quality parameters of a product and to identify surface defects based on white light phase-shifted deflectometry is described, e.g., in U.S. Patent Application Publication No. 2017/0227471. The device includes a screen which provides profile patterns with areas that form spatial light intensity profiles and a curved mirror arranged between the screen and a holder for providing a second light profile pattern. Like the setup shown in FIG. 1, the device described in U.S. Patent Application Publication No. 2017/0227471 requires an image recording unit to record a plurality of images to determine properties of the surface of the sample.
The setup shown in FIG. 1 begins to exhibit serious limitations when moving into a softmicroscopy regime; that is defocus blur begins to become a major limitation. In a typical deflectometry setup, such as the setup shown in FIG. 1, the camera has to be held at an angle to the portion of the surface to be inspected to be able to image reflected light coming from the illumination unit. As the object pixel size of the camera is decreased, and thus the useable depth of field also depreciates, the useable field of view begins to shrink significantly. The implications are that for imaging of large areas on a test surface, many more inspection “poses” are required, and thus the overall cycle time for the inspection of the test piece increases significantly.